This invention mainly concerns a method and device for analyzing step by step the very high frequency radiation beam of electromagnetic waves received on a given surface. The invention applies especially to a beam of such waves transmitted by a very high frequency transmitting antenna.
Such studies are particularly needed to assemble and use transmitting antennae.
For such a study either one of the following two methods is called upon.
1. The radiation characteristics of the transmitting antenna are drawn up by using other receiving antennae arranged like the transmitting antenna on an outer testing base. This method can only be used to the extent that the transmitting antenna and the receiving antennae, which will make it possible to design the characteristics, are adequately spaced (for instance, for an antenna with a span of 50 wavelengths 5,000 times the wavelength, or 500 meters for frequencies equal to about 3000 MHZ). Also, the studies are valid under such circumstances only if the landscape profile is conducive. Also, the environment cannot trigger parasitic reflection phenomena which cause interference. It is obvious that such an analytical method runs against major infrastructural difficulties with respect to implementation. Moreover, this method is very time consuming, and it requires several hundred hours for drawing up the characteristics of a transmitting antenna.
2. In view of the tediousness of the above method, a method is developed presently to deduce the radiation characteristics of an antenna from measurements of the electromagnetic field conducted in the immediate vicinity of the antenna. This is an indirect method, and the field measurement is carried out by way of an extremely sensitive probe which moves in front of the antenna being measured. The probe itself can consist of an open guide or of a dipole.
The problems surface at the level of the mechanical displacement system of the probe and of its electrical connections with the measuring receiver, which trigger disruptive parasitic reflections which can be eliminated by protecting them from absorbing systems, which complicates the system and increases the clutter.
Furthermore, the measurements must be conducted in perfectly marked points: the mechanical displacement system of the probe must be extremely accurate.
However, the basic restriction in this method lies in the slowness of the mechanical displacement system of the probe.
In present systems, the speed does not exceed 10 centimeters/second. As regards the control of a very high frequency square antenna which operates at 3000 MHZ with a side of 50 wavelengths, measurement time is five hours.
The invention is designed to allow for rapid and accurate measurement in a very economical way which permits the study of the very high frequency radiation beam of electromagnetic waves received on a given surface and applies especially to the study of a beam of such waves radiated by a very high frequency transmitting antenna, which does not offer any of the disadvantages and restrictions of the two known methods mentioned above.